Heat-resistant bearing material

ABSTRACT

A heat-resistant bearing material consisting of an austenitic iron matrix alloy should, under high temperatures, have good solid lubricant properties with a high heat resistance and a high creep resistance. To this end, an iron matrix alloy is used, containing a sufficient sulphur part for obtaining a solid lubricant action on the bearing surfaces thereof, and between 1 and 6 wt. % of at least one of the following alloy elements: tungsten (W), cobalt (Co), niobium (Nb), rhenium (Re), molybdenum (Mo), tantalium (Ta), vanadium (V), hafnium (Hf), yttrium (Y), zirconium (Zr), and/or comparably high-melting alloy elements.

The invention relates to a heat-resistant bearing material consisting of an austenitic iron matrix alloy, and here addresses the problem of making such a bearing material functionally reliable for use at high temperatures, especially at temperatures exceeding 600° C., in particular exceeding 850° C. The bearing material here is to exhibit solid lubricant properties, which are to be retained at the specified high temperatures to as high a degree as possible.

This object is achieved by means of a bearing material according to the characterizing features of claim 1

Advantageous alloys of such a bearing material are the subject matter of the subclaims.

The invention is based on the general idea of providing sulfur in a percentage amount that allows sulfides required for a lubricating effect to form within the alloy. Such a formation of sulfide within an austenitic matrix alloy intended to exhibit a high creep resistance and high strength at high temperatures is a contradiction in and of itself. This contradiction stems from the fact that, based on general expert knowledge, sulfides contained in such a material are disadvantageous for a high creep resistance and high strength at high temperatures because they constitute a structural disturbance, and must therefore be avoided. Therefore, the invention proposes something that runs absolutely counter to general expert knowledge with respect to the objective of obtaining a material that is highly creep resistant and strong in terms of temperature, and still exhibits lubricating properties even at high temperatures, and hence represents a surprising result not to be expected by an expert.

The drawing shows a few diagrams depicting characteristics for bearing materials according to the invention. The curves denoted in individual diagrams relate to a material according to claim 7 if marked A, and a material according to claim 8 if marked B.

EXPLANATION TO INDIVIDUAL DIAGRAMS

FIG. 1 a, 1 b

These diagrams show the creep behavior of alloys A and B during the gradual exposure of a sample in increments of 2 MPa, a retention period of 35 sec and when measuring the creep rate in the last 5 sec of the retention period, specifically in part a for a creep behavior at 700° C., and in part b for a creep behavior at 900° C.

FIG. 2

This diagram records the modulus of elasticity E and sheer modulus G for alloys A and B as a function of temperature.

FIG. 3

This diagram depicts the thermal expansion coefficient for alloys A and B as a function of temperature.

FIG. 4

This diagram records the hot hardness (in HV10) on the ordinate as a function of the temperature for alloys A and B.

FIG. 5

The ordinate shows the hardness (in HB 2.5/187.5) for alloys A and B after stored for a respective 2 hours and air-cooled as a function of temperature.

FIG. 6

This figure contains a table that indicates values for p =density, λ=heat conductivity, R_(p02)=expansion limit, R_(m)=tensile strength, E=modulus of elasticity for alloys A and B at respective room temperature.

All features described in the specification and the following claims can be significant to the invention both individually and taken together in whatever form. 

1. A heat-resistant bearing material that is an austenitic iron matrix alloy, consisting of: a sufficient sulfur percentage to achieve a solid lubricant action on bearing surfaces of the bearing material, and between 1% w/w and 6% w/w of at least one or more of the melting alloy elements: tungsten (W), cobalt (Co), niobium (Nb), rhenium (Re), molybdenum (Mo), tantalum (Ta), vanadium (V), hafnium (Hf), yttrium (Y), zirconium (Zr) and an alloy with a comparable melting point to the melting alloy elements; and wherein the following alloy composition is included, where the individual alloy elements are each indicated in % w/w: C=0.4-0.6 Cr=18-27 Nb=1.4-1.8 Ni=12-22 S=0.2-0.5 Si=2.9-3.2 Residue=Iron Contaminants or unspecified alloy elements up to
 3. 2. The bearing material according to claim 1, wherein the following alloy composition is included, where the individual alloy elements are each indicated in % w/w: C=0.4-0.6 Cr =18.5-20.5 Nb =1.4-1.8 Ni =12.5-14 S =0.25-0.45 Si=2.9-3.15 Residue=Iron Contaminants or unspecified alloy elements up to
 3. 3. The bearing material according to claim 1, wherein the following alloy composition is included, where the individual alloy elements are each indicated in % w/w: C=0.4-0.6 Cr=24.5-26.5 Nb=1.4-1.8 Ni=19.5-21.5 S=0.25-0.45 Si=2.9-3.15 Residue=Iron Contaminants or unspecified alloy elements up to
 3. 4. The bearing material of claim 1, wherein a paddle bearing ring is constructed of the bearing material. 